This invention relates to a control circuit for controlling reproduced tone characteristics and, more particularly, to a control circuit capable of prestoring sound field characteristics to be imparted to a reproduced tone and frequency characteristics of the reproduced tone in combination and reproducing these characteristics simultaneously.
In recent audio techniques, various attempts have been made for reproducing a sound field in a listening room. These attempts are directed to realization in a listening room of reproduction of a musical tone in an atmosphere simulating an actual hall or concert. In an audio system for realizing such sound field, as shown by the plan view of FIG. 9, there are provided main loudspeakers a and b of left and right channels for reproducing direct tones and sound field effect loudspeakers c, d, e and f of front left, front right, rear left and rear right channels for reproducing sound field effect tones (i.e., reflected tones and reverberating tones). If necessary, a television monitor g is provided between the main loudspeakers a and b. To the main loudspeakers a and b are supplied reproduced tones from an input source, imparted with frequency characteristics if necessary. To the sound field effect loudspeakers c, d, e and f are supplied reflected tones and reverberating tones produced on the basis of the reproduced tones from the input source.
For producing sound field effect tones, they may be produced by a simple method using a reverberator or a delay machine. For realizing a sound field simulating a real sound field more closely, there is a system in which sound field effect tones are produced by superposing a tone signal from the input source on reflected tone data prepared by measuring reflected tones in an actual sound field.
This sound field effect is obtained by, as shown in FIG. 3, issuing an impulse signal from a stage of an acutal hall, church, studio or other environment, catching multiple initial reflected sound waves arriving from four directions to a listening point by a four-point (i.e., four-channel) microphone placed at a listener's seat, storing, by a digital processing, hypothetical tone source distribution on the basis of data collected by the microphone with respect to each direction in which the reflected sound waves have arrived, reading out the stored data in the reproduction mode and combining it with an input tone signal thereby to reproduce a sound field which is analogous to one which was measured and stored. This sound field effect system is disclosed in the specification of Japanese Patent Application No. 99244/1985.
The feature of this system is that the reflected sound is not issued in only a direction in which the loudspeaker is disposed as in a conventional processor but, directions, amounts of delay and levels of multiple reflected sounds are simulated in three-dimentional space by using four loudspeakers (c, d, e and f in FIG. 9). For this purpose, the four loudspeakers c, d, e and f are disposed at four corners of a listening room.
Accordingly, the sound field processor does not produce a sound field pattern by utilizing components contained in the input tone signal but selects and applies one of previously stored, ready-made sound field patterns which is most closely simulating a desired sound field. If, for example, 88 different data (22 for each loudspeaker) are stored as initial reflected waves, sound fields simulating various environments such as a hall can be realized in a listening room with high fidelity.
For realizing a sdund field more closely in the reproduction of a sound field employing the initial reflected sound data, control of reproduced frequency characteristics of an input tone signal per se is important in addition to setting of time region by delay time and space image by reflected sound waves. A sound field can be reproduced with high fidelity by realizing multi-dimensional setting of time, space and frequency characteristics.
In the prior art sound field effect reproduction system using initial reflected sound data, however, it was possible to prestore set conditions of time and space and reproduce and impart them to an input tone signal instantaneously but it was not possible to prestore a controlled state of reproduced frequency characteristics of the input tone signal per se in combination with the set conditions of time and space. Accordingly, for creating an optimum sound field, it was necessary in the prior art system to set frequency characteristics of the input tone signal matching with a particular sound field each time this sound field is to be reproduced.
It is, therefore, an object of the present invention to provide a control circuit for controlling reproduced tone characteristics capable of storing set conditions of sound field effect characteristics to be imparted to a reproduced tone signal and frequency characteristics of the tone signal per se in combination and reproducing these characteristics simultaneously.